Separable effects of human Kvβ1.2 N‐ and C‐termini on inactivation and expression of human Kv1.4
- 1 October 1998
- journal article
- Published by Wiley in The Journal of Physiology
- Vol. 512 (2) , 325-336
- https://doi.org/10.1111/j.1469-7793.1998.325be.x
Abstract
The Kvβ subunits of voltage‐gated K+ channels alter the functional expression and gating of non‐ or slowly inactivating Kvα1 subunits via two separate domains. To determine how Kvβ subunits modulate a rapidly inactivating Kvα1 subunit, we did two‐microelectrode voltage clamp experiments on human Kv1.4 voltage‐gated K+ channels expressed heterologously in Xenopus oocytes. In addition we tested a slowly inactivating mutant of Kv1.4 lacking amino acids 2–146 of the N‐terminal α‐ball domain (Kv1.4ΔN2‐146). Kv1.4 or Kv1.4ΔN2‐146 were co‐expressed with either rat Kvβ2 or human Kvβ1.2. To separate domain effects, we also used a mutant of Kvβ1.2 lacking the unique 79 amino acid N‐terminal β‐ball domain (Kvβ1‐C). For the mutant Kv1.4ΔN2‐146 we found that Kvβ1‐C or Kvβ2 increased current amplitude without altering activation or inactivation. By contrast Kvβ1.2 produced rapid inactivation and slowed deactivation due to block produced by the β‐ball. The β‐ball also increased the rate of C‐type inactivation in 5 mm, but not 50 mm, external K+ consistent with an effect of blockade on K+ efflux. For Kv1.4, Kvβ1‐C produced a voltage‐independent increase in the rate of inactivation and shifted the inactivation curve to more hyperpolarized potentials, but had no effect on deactivation. Kvβ1‐C, Kvβ2 and Kvβ1.2 slowed recovery from inactivation similarly, thereby excluding involvement of the β‐ball. Kvβ1.2 produced an additional more rapid, voltage‐dependent component of inactivation, significantly reduced peak outward current and shifted steady‐state inactivation towards hyperpolarized potentials. Yeast two‐hybrid studies showed that α‐β interaction was restricted to the N‐terminus of Kv1.4 and the C‐terminus of Kvβ1.2 or Kvβ2. Direct interaction with the α‐ball did not occur. Our interpretation is that Kvβ1‐C and Kvβ2 enhanced N‐type inactivation produced by the Kv1.4 α‐ball allosterically. We propose that Kvβ1.2 has three effects on Kv1.4, the first two of which it shares with Kvβ2. First, Kvβ1‐C and Kvβ2 have a current‐enhancing effect. Second, Kvβ1‐C and Kvβ2 increase block by the α‐ball allosterically. Third, the β‐ball of Kβ1.2 directly blocks both Kv1.4 and Kv1.4ΔN2‐146. When both α‐ and β‐balls are present, competition for their respective binding sites slows the block produced by either ball.Keywords
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